The present invention relates to impedance transforming elements, and in particular to segmented and interdigitated integrated coupled transmission line elements.
The use of twisted pairs of copper wires to form coupled transmission line elements is well known. These transmission line elements may be used to create balanced and unbalanced transmission lines, balanced-unbalanced (balun) transmission lines, and current and voltage inverters. Examples of the use of conventional transmission line elements are presented in C. L. Ruthroff, xe2x80x9cSome Broad-Band Transformers,xe2x80x9d Proceedings of the IRE (Institute for Radio Engineers), vol. 47, pp. 1337-1342 (August 1959), which is incorporated herein by reference. These transmission line elements are typically found in forms that are useful in frequency bands through UHF.
The use of such transmission line elements in integrated circuits such as RF power amplifiers and low noise amplifiers that operate at higher than UHF frequencies is desirable. However, the incorporation of these conventional transmission line elements into RF devices such as cellular telephones is not competitively feasible due to size and cost. Moreover, conventional coupled transmission line elements are not suitable for use in the desired frequency range.
Therefore, a need has arisen for a coupled transmission line element that addresses the disadvantages and deficiencies of the prior art.
A transmission line element in accordance with this invention comprises a plurality of metal layers that are formed in an integrated circuit chip. Each of the metal layers is separated from an adjacent metal layer by a dielectric layer. In a bifilar embodiment, a first conductor comprises at least two transmission lines in different metal layers; and a second conductor comprises at least two transmission lines also in different metal layers. The transmission lines in the first and second conductors run parallel to each other. A plurality of interconnects are located at predetermined positions along the conductors, each of the interconnects containing an electrical connection between the transmission lines in the first conductor and an electrical connection between the transmission lines in the second conductor. At least one transmission line in the first conductor is edge-coupled to at least one transmission line in the second conductor and broadside-coupled to at least one other transmission line in the second conductor.
In addition, at least a second transmission line in said first conductor may be edge-coupled to at least one transmission line in said second conductor and broadside-coupled to at least one other transmission line in said second conductor.
The first and second conductors may be formed in the shape of a spiral or a variety of other shapes.
At least one of the interconnects may comprise a via through the dielectric layer, a first tongue extending to the via from one of said transmission lines and a second tongue extending to the via from another one of said transmission lines.
In one bifilar embodiment the first conductor comprises two transmission lines and the second conductor comprises two transmission lines. Alternatively, the first conductor comprises three transmission lines and said second conductor comprises three transmission lines.
In a trifilar embodiment the transmission line element comprises a third conductor, and each of said first, second and third conductors may comprise three transmission lines.